1. Field of the Invention
This invention generally relates to a damper mechanism. More specifically, the present invention relates to a damper mechanism for transmitting a torque while absorbing and damping torsional vibrations.
2. Background Information
A damper mechanism used in a clutch disk assembly of a vehicle is formed of, e.g., an input rotary member, an output member, and an elastic coupling mechanism. The input rotary member is releasably coupled to an input flywheel. The output rotary member is coupled to an input shaft of a transmission. The elastic coupling mechanism elastically couples the rotary members in a rotating direction. The input rotary member is formed of a clutch disk and a pair of input plates fixed to the clutch disk. The output rotary member is formed of a hub, which is unrotatably and axially movably coupled to the transmission input shaft. The hub is formed of a cylindrical boss spline-engaged with the transmission input shaft and a radial flange formed around the boss. The elastic coupling mechanism is formed of a plurality of elastic member assemblies. Each elastic member assembly is formed of a coil spring only or a combination of a coil spring and seat members arranged on the opposite ends thereof. Each elastic member assembly is arranged in a window aperture formed in the flange, and is supported at its opposite ends in the rotating direction. Each elastic member assembly is supported in various directions by edges of windows formed in the input plate pair.
In the structure described above, when the input plate pair rotates relatively to the hub, the coil springs are compressed in the rotating direction between the input plates and the hub. Thereby, torsional vibrations supplied to the clutch disk assembly are absorbed and damped by the damper mechanism.
In general, noises generated from a drive system due to torsional vibrations are classified into groups each including noises during idling, noises during constant-speed driving, noises during acceleration and deceleration, and muffled or confined noises. For absorbing the torsional vibrations, which may cause these noises, it is therefore necessary to determine appropriate torsion characteristics in the damper mechanism. Therefore, conventional damper mechanisms have employed two-stage characteristics, in which a low rigidity and a low hysteresis torque are achieved in a region of a small torsion angle for absorbing vibrations during idling. In these conventional two-stage characteristics, the region of high torsion angles may be divided into a region exhibiting an intermediate rigidity and a high hysteresis torque for absorbing muffled noises as well as a region exhibiting a high rigidity and a high hysteresis torque for absorbing vibrations and noises during acceleration.
In an FF (Front-engine and Front-drive) vehicle, a drive system has a high rigidity so that a resonance point remains in a practical operation range even if the torsion rigidity is reduced for the purpose of improving performances for noises and vibrations. Characteristics of engine speed variations are different between the positive (acceleration) side and the negative (deceleration) side, but no difference is present in the conventional torsion characteristics between the positive and negative sides. Therefore, even if good damping performances can be achieved on one side, good damping characteristics cannot be achieved on the other side. Thus, good damping performances cannot be achieved overall.
In connection with the vibration damping performances relating to variations in rotation speed of the transmission with respect to the engine rotation speed, the hysteresis torque can suppress resonance on the positive side, but cannot achieve good damping rate in a positive range higher than the resonance point or throughout the whole negative range. Conversely, the low hysteresis torque can achieve good damping rates in the positive range higher than the resonance point and throughout the whole negative range, but can cause large variations in rotation speed at the positive resonance point.
As mentioned above, if the torsion characteristics on the positive side are similar to those on the negative side, and particularly if no difference is present in hysteresis torque between the positive and negative sides, it is impossible to provide the torsional damping characteristics, which are preferable over the whole range.
In view of the above, there exists a need for damper mechanism which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the invention is to achieve preferable vibration damping characteristics by providing different torsion characteristics on the positive and negative sides.
According to a first aspect, a damper mechanism includes a first rotary member, a second rotary member, a plurality of elastic members and a friction generating mechanism. The second rotary member is rotatable with respect to the first rotary member. The plurality of elastic members are arranged to be compressed when relative rotation occurs between the first and second rotary members in the rotating direction, and exhibit a higher rigidity on the positive side of the torsion characteristics than the negative side. The friction generating mechanism is arranged to generate friction when relative rotation occurs between the first and second rotary members, and generates a larger friction on the positive side of the torsion characteristics than the negative side.
This damper mechanism can provide characteristics, in which the rigidity and hysteresis torque are high on the positive side (acceleration side) of the torsion characteristics, and are low in the negative side (deceleration side) of the torsion characteristics. As a result, it is possible to suppress variations in rotation speed, which may occur when passing through the resonance point, on the positive side of the torsion characteristics. Also, good damping rates can be achieved throughout the negative side of the torsion characteristics.
According to a second aspect of the present invention, the damper mechanism of the first aspect further has a feature such that the friction generating mechanism has a first friction generating portion for generating friction at least on the negative side of the torsion characteristics, and a second friction generating mechanism for generating friction on the positive side of the torsion characteristics. Since the damper mechanism of this aspect has two friction generating portions for generating the friction on the positive and negative sides, respectively, the hysteresis torque on each of the positive and negative sides can be controlled independently of each other.
According to a third aspect of the present invention, the damper mechanism of the second aspect further has a feature such that the first friction generating portion operates on the positive and negative sides, and the second friction generating portion operates only on the positive side. In this damper mechanism, the first and second friction generating portions operate on the positive side, and only the first friction generating portion operates on the negative side.
According to a fourth aspect of the present invention, the damper mechanism of the second or third aspect further has a feature such that the first friction generating portion has a first friction member for generating friction between the first and second rotary members, and a first biasing member for biasing the first friction member. The second friction generating portion has a second friction member for generating friction between the first and second rotary members, and a second biasing member for biasing the second friction member. In this damper mechanism, each of the friction generating portions has a friction generating member and a biasing member. Therefore, when changing the rotational direction of the rotary members, the hysteresis torque can be independently controlled on the positive and negative sides.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.